1. The Field of the Invention
This invention relates generally to calibrating and tracking of inertial measurement units, and specifically relates to systems, methods, and apparatus for three-dimensional tracking of intermittent motion with the aid of an inertial measurement unit.
2. Background and Relevant Art
An Inertial Measurement Unit (IMU) is a device that can report on the inertial status of a moving body including the acceleration, velocity, orientation, and position of the moving body. The use of an IMU may facilitate tracking of movement of a body by integrating the acceleration and the angular velocity measured by the IMU. In some instances, the IMU can supplement or replace alternative tracking systems, such as a global positioning system (GPS). One advantage that an IMU may have over other tracking systems, such as a GPS, is that the IMU is self-contained and does not require input or feedback from an external device. Hence, an IMU can continue tracking movement and position of a body in locations where a GPS signal may be unavailable.
Typically, an IMU utilizes a combination of accelerometers and gyroscopes that can determine and quantify linear acceleration and angular velocity, respectively. The values obtained from the IMUs gyroscopes can be processed to obtain the pitch, roll, and heading of the IMU and, therefore, of the body with which the IMU is associated. Signals from the IMU's accelerometers also can be processed to obtain velocity and displacement of the IMU. Accurate results, however, may depend on the quality of the IMU. A higher precision IMU typically comes at a higher price and may come with increased weight and size, as compared with a generally lower-precision IMU.
The size and price of IMUs utilizing low-cost, miniaturized inertial sensors may make such devices attractive for applications where, for example, smaller size and lower weight are important. A typical example is the use of IMUs based on microelectromechanical systems (MEMS) inertial sensors. Modern manufacturing techniques have made MEMS IMUs less expensive and have increased their durability. Unfortunately, typical low-cost, consumer-grade MEMS IMUs currently have lower precision than is needed to allow them to provide accurate position information. In fact, error accumulation and growth during the operation of consumer-grade MEMS IMUs can easily render their time-integrated output signals highly unreliable within a matter of seconds.
More specifically, consumer-grade MEMS IMUs are commonly plagued with manufacturing deviations as well as other inherent problems. For instance, a typical consumer-grade MEMS IMU can suffer from scale factor nonlinearlity, anisotropic sensitivity, gyroscope acceleration sensitivity, output noise, parameter drift, or other issues, which can lead to unbounded error growth. Consequently, the advantages of the MEMS IMU's size and cost are frequently overshadowed by and/or cannot be adequately realized due to the inherent errors in its output. Although various attempts have been made to address various inadequacies related to the inherent error in MEMS IMUs' output, conventional systems may not produce sufficiently accurate results that can be used to track velocity, position, and/or orientation of the MEMS IMU in a three-dimensional space. These same limitations, in whole or in part, can also apply to IMUs based on other technologies that sacrifice accuracy in exchange for reduced size, weight, and/or cost or other desirable characteristics.
Accordingly, a need exists for systems, methods, and apparatus for three-dimensional tracking of intermittent motion with the aid of an inertial measurement unit.